2021年四川泸县MS6.0地震震源性质及震前区域应力场特征

为了解2021-09-16四川泸县M_S6.0地震的发震机理，加强对四川盆地内地震活动性的认识，基于四川及周边地区地震台网的宽频带地震资料，利用CAP方法反演获得泸县地震的震源机制解和矩心深度；同时，基于震前四川盆地内155个震源机制解，利用MSATSI程序反演得到泸县地震震前四川盆地内的构造应力场。结果显示，泸县地震矩心深度为3 km，矩震级为M_W5.3，滑动性质为纯逆冲。震中附近震前构造应力最大主压应力和中间主压应力都近乎水平，最大主压应力在震中附近走向101°，此构造应力状态下，优势滑动断层为纯逆冲性质，与泸县地震震源机制一致。根据震源位置和性质、震前构造应力场及震中附近的断层性质推测，泸县地震发震断层不是华蓥山断裂，而是其分支和余脉之间极浅的盖层滑脱型断层。

Source Properties and Characteristics of Tectonic Stress Field before the September 16, 2021, Luxian MS6.0 Earthquake in the Sichuan Basin

Based on the seismic data for Luxian M_S6.0 earthquake provided by Sichuan and surrounding provinces’ seismic network, using the CAP inversion method, we calculate source parameters, like focal depth, moment magnitude and focal mechanism. From the focal mechanism of 155 events occurring in those regions, using the MSATSI code, we derive the tectonic stress field in the Sichuan basin before the earthquake. The results indicate that the focal depth of the Luxian earthquake is 3 km, and the moment magnitude is M_W5.36 with pure thrust faulting rupture. Tectonic stress before the event shows that the directions of both maximum and the intermediate principal compressive stress are almost horizontal, and the strike angle of the maximum principal compressive stress is about 101° near the epicenter. Under such stress framework, the optimal sliding fault is pure thrust, completely consistent with the focal mechanism of the Luxian earthquake. This event faulting is mainly controlled by the lateral force, suggesting that the southwestern part of the Sichuan basin is involved in the eastward expansion of the Tibetan plateau. This event is the result of activation of the shallow detachment fault under this tectonic background. Based on the source properties and background stress, we infer that the seismogenic fault of the Luxian earthquake may not be the Huayingshan fault, but a very shallow caprock slip-type fault between its branches.